The present invention relates to a vehicle suspension apparatus having a contraction/expansion body including a cylinder and a hollow rod telescopically coupled to the cylinder in a substantially coaxial relation so as to reciprocate therewith and formed therein an internal space of variable volume, the internal space being separated into a gas chamber filled with a gas and an oil chamber filled with a working oil; a restriction member arranged in the oil chamber to be substantially perpendicular to an axis of the construction/expansion body and having an orifice to allow passage for the working oil occupied with the orifice therebetween; an auxiliary container for containing a gas therein; and a channel for coupling through a valve the gas chamber of the internal space of the rod and a gas chamber of the auxiliary container.
Most conventional vehicle suspension apparatuses use metallic springs such as coil or leaf springs. However, vehicle suspension apparatuses using hydropneumatic actuators in place of the metallic springs have become prevalent recently. In such a suspension apparatus using a hydropneumatic actuator, the buffer function, obtained by the resiliency of the gas, and the damping force, obtained by flow resistance upon the flow of working oil through an orifice, are used to provide the damping effect and the braking force of the suspension apparatus. However, in a hydropneumatic actuator of this type, a spring constant is determined depending upon the pressure of the sealed gas and the volume of the gas chamber. Therefore, unless the gas pressure or volume is changed properly, optimal damping characteristics cannot be obtained in accordance with various travel conditions of a vehicle.
In order to solve this problem, it has been proposed to use an auxiliary container with an inner gas chamber in addition to a conventional hydropneumatic actuator and to communicate the two gas chambers with each other by means of a valve, thereby changing an effective volume serving as a gas chamber and changing the spring constant of the suspension apparatus using the gas pressure.
However, as a result of studies made, it has been found out that the function of a vehicle suspension apparatus can be improved by changing the damping force of an orifice in accordance with the travel condition in addition to changing the spring constant of the apparatus.